The present invention relates generally to a loudspeaker, and more particularly to a loudspeaker that generates sound using piezoelectric material.
The present invention relates to a loudspeaker using piezoelectric or electroactive materials. Such materials, as is well known in the art, have the desirable property of converting electrical energy into mechanical energy, by undergoing a controllable amount of deformation when subjected to an applied electric field. Examples of electroactive materials include, among others, piezoelectric ceramics such as the lead zirconate titanate family (commonly known as PZT) with all its variously substituted and doped relatives, electrostrictive ceramics such as certain compositions of lanthanum doped PZT (PLZT) or lead magnesium niobate (PMN), and piezoelectric polymers such as polyvinylidene fluoride (PVDF).
In the speakers, the piezoelectric or electroactive material may be arranged in a variety of ways, including unimorph or bimorph benders. Benders are devices wherein the controlled strain of one or more layers is resisted by other layer or layers, resulting in a bending deformation. The most common benders are classified as unimorphs, which contain one active layer, and bimorphs, which contain two active layers. More recently another type of bender was introduced under the name of RAINBOW(copyright) (Reduced and Internally Biased Oxide Wafer) and possessing certain attractive performance characteristics. The RAINBOW(copyright) wafer is described in detail in U.S. Pat. No. 5,589,725, entitled xe2x80x9cMonolithic Prestressed Ceramic Devices And Method For Making Same,xe2x80x9d which is incorporated by reference herein.
One of the uses of piezoelectric material known in the art is in loudspeaker applications. For example, Kumada et al., U.S. Pat. No. 4,352,961, discloses a flat panel speaker comprising a transparent resonator plate and a plate of a piezoelectric material held between a pair of electrodes. The piezoelectric material plate excites the resonator causing it to emit sound. Kumada requires the resonator plate and the piezoelectric material plate to be transparent, thus limiting the types of material that can be utilized as speakers. Furthermore, Kumada requires attachment at the edges of the resonator plate, which decreases the sound quality of the speaker.
In Takaya, U.S. Pat. No. 4,969,197, a piezoelectric speaker is disclosed that creates an acoustic pressure in air by piezoelectrically driving a diaphragm. The diaphragm is an assembly of two resin foam plates facing each other. Each resin foam plate has a recess and a projecting member at the center of the recess bottom. The piezoelectric driver is accommodated in the space made of the two recesses while being interposed and supported by the projecting members. One of the disadvantages of Takaya is that it does not teach the best configuration choice for projecting members. Another disadvantage is that Takaya does not teach the best bender shape for optimizing sound quality.
The present invention avoids the problem of the known piezoelectric speakers by utilizing the favorable acoustic properties of various elastic bases. Unlike Kumada, the present invention is not limited to transparent material. By way of example, the elastic base may include a computer monitor housing, a television set, any welded structure such as an automobile cargo bay or file cabinet, a plastic box, a dry wall or building frame, a small appliance, or a bicycle helmet. In all these applications an acoustical pressure with higher dB level is generated by a significantly larger area of a driven object. In this manner, an entire structure becomes a speaker with numerous acoustical properties dependent upon the material and shape of the attached elastic base.
The feature of the present invention of utilizing an attached elastic base for acoustical output allows speakers to be conveniently designed in a very low profile, planar shape to fit even highly confined enclosure volumes. By way of example, the piezoelectric speaker can fit within a slot, such as in the case of a bicycle helmet application, or the piezoelectric speaker can fit within a thin layer space of approximately 0.040xe2x80x3 in a computer keyboard application.
The present invention also provides sound quality superior to that of the prior art. The limitation of the Takaya device is overcome by using a rigid acoustical linkage that will not interfere with the transmission of vibrations. Furthermore, unlike Kumada, the present device does not require attachment at the edges. The attachment of the acoustical linkage at a single point, as disclosed herein, allows the acoustical properties of the speaker to be adjusted by varying the peripheral radii of curvature.
Accordingly, it is a primary object of the present invention to overcome one or more disadvantages and limitations of the prior art. A significant object of the present invention is to provide a piezoelectric speaker that is easily and inexpensively manufactured. It is another object of the present invention to provide a piezoelectric speaker that is easily secured to an existing structure.
According to a broad aspect of the present invention, the speaker includes an elastic base, a piezoelectric material bender, and an acoustical linkage mounted to both the elastic base and the bender and serving to interconnect the elastic base and the bender The acoustical linkage is fabricated from a rigid material and is mounted to the bender near the geometric center or any other acoustically favorable position on the bender. If needed, the bender may be encapsulated in a case. The elastic base may include a computer keyboard, a bicycle helmet or any other acoustically favorable elastic base.
A feature of the present invention is that the piezoelectric speaker is easily manufactured.
Another feature of the present invention is that the piezoelectric speaker has a broad frequency range.
Another feature of the present invention is that the piezoelectric speaker is easily adapted to existing structures.
These and other objects, advantages and features of the present invention will become readily apparent to those skilled in the art from a study of the following description of an exemplary preferred embodiment when read in conjunction with the attached drawing and appended claims.